I think your question boils down to, can I load data into MIME::Lite without first putting it into a file, and the answer is yes.

From MIME::Lite :

You can specify each message part as either the literal data itself (in a scalar or array), or as a string which can be given to open() to get a readable filehandle (e.g., "<filename" or "somecommand|").

If getting the image data into a scalar or whatever is your problem, the answer would depend on how you're letting people upload these images and what modules you're using to achieve that.

--Pileofrogs